Hopefully the Griff chief won't complicate negotiations too much. As Mana seems to have picked up on, he has every right to attend since they've invaded his people's land as well.
On the other hand he is liable to be somewhat coarse and probably has very little grasp of the politics and niceties involved. And then there's the fact, so easy to forget, that Claw is strictly a princess rather than a prince. If that fact is uncovered (Mana, for instance, doesn't know about it yet) that is likely to cause complications wrt Claw's legitimacy in the eyes of the King. Which forms the primary basis of the ceasefire.
They really are very lucky the prince returned; even small skirmishes involving armies are not known for letting everyone on either side go home. I wonder if it will end up weighing on the faculty that if things had gone further, even if they had won, they'd have had both Gardenians and griffins to bury...